I am building 4 way active speakers and am going to add approx 30 uF capacitor to protect the tweeter from low freq and DC current. Is quality important in this situation? I am using a high quality Scanspeak tweeter, so don't want to limit it, but on the other hand no point buying a quality cap if it wont make any difference in this scenario. It will be cutting off way below the active crossover point.
You could do that, from what I have managed to find online it seems that the general consensus is to go 2 octaves below the crossover point so it has no direct impact. I was thinking of just using a cheap Dayton Audio DMPC-33 33uF 250V Polypropylene Capacitor.
Tweeter is 8 ohm (ScanSpeak D2908/7140 Beryllium Dome) so that should cut off at 600 Hz (+2 octaves being 2400 Hz)
Tweeter is 8 ohm (ScanSpeak D2908/7140 Beryllium Dome) so that should cut off at 600 Hz (+2 octaves being 2400 Hz)
Every crossover I've seen has at least a series cap for the tweeter already to prevent low frequencies and DC (the ultimate low frequency). Why do you need another?
G²
Why not use a lower value capacitor and use it (I think as asusliver was saying) as part of the crossover? This would "require" a high quality cap, but at a lower capacitance the cost increase wouldn't be as much, and a lower value will better protect the tweeter.
The OP said "active" meaning the crossover is done at line-level, before the amplifier (and there's an amplifier for each driver). The amp's output would connect directly to the tweeter without the cap.
I am going for an active crossover, so this will be the only component between the amp and the driver (no passive crossover)
Yes, but what if....I have way cheaper tweeters than him and I am still going to use a capacitor.
He wants his 8 ohms tweeter to be crossed at 2400hz, I would(but I might be wrong)use an 10uf(or more) /100v(or more) capacitor , according to this :
ERSE - Crossover Calculator - First Order 2 Way
The size for such cap will not be that big.
I am going to use a DSP for the crossover so from what I can understand will be able to adjust the phase to compensate without too many issues. Wouldn't know how to build a DC protection circuit I am afraid
Yup, make it one of the poles of the tweeter crossover, then measure the tweeter/design the DSP xover with the cap in place and design around it, as I'm sure it'll be close enough to work just fine. Provides the most protection of any solution, too. Use a quality cap.
Sounds like the best option, especially to keep the cost down. What size would you recommend, the DSP allows for 24 db high pass slope so a 6 db(?) slope from the cap is going to start having an impact if too close to the active crossover frequency isn't it? (I am not that knowledgeable on crossover design that is why I decided to go DSP).
Looking at local suppliers I can get "18uF 700V Mundorf Supreme EVO Oil". Using the crossover calculator mentioned above that is about 1100 Hz.
Looking at local suppliers I can get "18uF 700V Mundorf Supreme EVO Oil". Using the crossover calculator mentioned above that is about 1100 Hz.
No I mean *to* have it impact on the active crossover! Use any of the thousand freebie crossover simulators for your tweeter driver impedance curve and "design" a 1st order to be a little lower than your target 4th order Xover. Ultimately you'll end up with 3rd order DSP and a 1st order passive.
I see, in that case I might just get a few cheap ones test the resulting response curve with my tweeters and then once I work out the best fit buy a couple of quality ones of just that uF value.
From what I have read they can be used in parallel to add up to different values for testing purposes (e.g. 12uF + 6uF = 18uF etc). Can buy 1,3,6,12,24 for not too much and that will allow almost any sensible value.
From what I have read they can be used in parallel to add up to different values for testing purposes (e.g. 12uF + 6uF = 18uF etc). Can buy 1,3,6,12,24 for not too much and that will allow almost any sensible value.
Used to use a $$$ Mundorf Supreme as protection for my tweeter in an active setup similar to your description (2x oversized) till I tough that using a fusible would create no phase shift at all and still protect the tweeter...
The $0.25 fuse blew the Mundorf apart like it was a cheap electrolytic.
I'm using 0.75A fusible and it protect the tweeter (95db efficient) as good as a capacitor given you have no DC offset from upstream.
0.3A and 0.5A fuse induced loss as the resistance of the fusible filament was a tad too high for my application and the fuse acted like a low value resistor.
Try it, it will beat any capacitor anybody can possibly suggest.
Let me know your results
The $0.25 fuse blew the Mundorf apart like it was a cheap electrolytic.
I'm using 0.75A fusible and it protect the tweeter (95db efficient) as good as a capacitor given you have no DC offset from upstream.
0.3A and 0.5A fuse induced loss as the resistance of the fusible filament was a tad too high for my application and the fuse acted like a low value resistor.
Try it, it will beat any capacitor anybody can possibly suggest.
Let me know your results
I usually use a very large electrolytic with a small value film in parallel. The electrolytic is large enough to not affect the tweeter's passband, so a value of 80-100uF is usually sufficient, with a 10-15uF film cap. Never noticed a sonic issue compared to direct connection in either distortion, FR or phase.
With a cap in the passband plus active filtering, you are essentially manipulating the phase response of the speaker so it can be done but it's not something you can eyeball and get right, math is needed. Servos, PTCs and fusibles all work well for protection as do lightbulbs, all have been used for similar tasks. But all have their own drawbacks and quirks, so choose your poison.
With a cap in the passband plus active filtering, you are essentially manipulating the phase response of the speaker so it can be done but it's not something you can eyeball and get right, math is needed. Servos, PTCs and fusibles all work well for protection as do lightbulbs, all have been used for similar tasks. But all have their own drawbacks and quirks, so choose your poison.